Among the central questions in developmental biology is how the genome of an organism specifies its development. that is, for a given organism, what is the nature of the genetic program that directs the pattern of cell divisions, the generation of diverse cell types and the morphogenesis of such cell types into specialized structures? The long- term goal of the research described in this proposal is to understand how developmental decisions are specified in the nematode Caenorhabditis elegans, which provides a relatively simple well-characterized model system for metazoan development. this proposal focusses on the process of sex determination which is one of the most comprehensive of determinative events in C. elegans development. The developmental control gene her-1 functions during development to determine sexual phenotype. The level of her-1 activity determines via a regulatory hierarchy involving at least six other sex-determining genes, which pathway of sexual differentiation (male or hermaphrodite) the C elegans embryo takes. The level of her-1 activity is controlled by the primary sex-determining signal the X chromosome to autosome (XA) ration. The goal of this proposal is a detailed molecular analysis of the her-1 gene, specifically examining how the XA ration controls the level of her- 1 activity and how the her-1 gene in turn exerts its effect on sex determination. The her-1 gene has been cloned and sex-specific transcripts identified. The specific aims of this proposal are: (1) A detailed characterization of the her-1 transcripts including their temporal and spatial expression. (2)Nucleotide sequencing of genomic and cDNA her-1 clones, (3) A detailed molecular analysis of the 27 mutant her-1 alleles including a) an examination of her-1 transcripts in these mutant strains and b) a determination of the precise location and nature of the mutation in the two dominant her-1 alleles and selected recessive alleles (4) Identification of factors that bind to regulatory elements of the her-1 gene and an analysis of such factors using her-1 and other mutant strains 95) Molecular cloning of genes that directly regulate her-1 expression i,e., that code for her-1 binding factors, and (6) Molecular characterization of her-1 and her-1 binding-factor clones using the technique of transformation with exogenous DNA.